Process and plant for the thermal treatment of fine-grained solids

ABSTRACT

A process for at least one of a chemical and a physical treatment of fluidizable substances in a reactor. The process includes introducing a hot gas into an interior of the reactor through a gas supply tube and cooling at least one of the hot gas and the gas supply tube with a coolant. The cooling is performed by contacting the hot gas with the coolant so as to provide a temperature of a wall of the gas supply tube at least 50° C. lower than a temperature of the gas at an inlet of the gas supply tube facing away from the interior of the reactor.

This invention relates to a process for the chemical and/or physical treatment of fluidizable substances in a reactor, in particular in a fluidized-bed reactor, wherein hot gas, in particular the waste gas of a combustion chamber upstream of the reactor, in which fuel and combustion air are burnt at temperatures of 1000 to 1500° C., is introduced into the reactor interior via a gas supply tube. Furthermore, this invention relates to a plant for the thermal treatment of granular solids.

From DE 102 60 741 A1, a process as mentioned above and a respective plant are known, in which hot gas with a temperature of about 1130° C. is generated in a combustion chamber upstream of the reactor and supplied to the reactor. Inside the reactor, this hot gas then can be cooled to about 750° C., for instance by contact with the cooler substances to be treated and/or by mixing with fluidizing gas. However, the hot gas enters the reactor with a comparatively high temperature and in said reactor gets in contact with the solids to be treated, which on the one hand can lead to local overheating and on the other hand also greatly stresses the components of the reactor.

From EP 0 630 683 B1, it is furthermore known to introduce hot gas into a reactor, wherein the hot gas is cooled by solid particles inside the reactor. In addition, cooling panels can be provided in the reactor.

In some applications, for instance when calcining clay, the temperature inside the reactor should not be above 700° C. Therefore, for instance in the processes mentioned above, problems arise in such applications when the fluidizable substances to be treated get in contact with the distinctly hotter waste gas of a combustion chamber. For such applications, such as the calcination of clay, conventional inexpensive fuels such as natural gas, petroleum or coal therefore cannot directly be burnt in the reactor. Thus, only a fuel such as butane, which ignites at lower temperatures, can also be used for a direct combustion inside the reactor space. Such fuels, however, which burn at lower temperatures, are comparatively expensive.

In other applications, hot gases are created and will be used in the downstream process parts as hot as possible, in order to introduce the heat into these process parts.

Furthermore, the above-mentioned plants, in which hot gas is introduced into the reactor interior with temperatures of 500 to 1600° C., in particular 1000 to 1500° C., are expensive to manufacture, as the gas supply tube, through which the waste gas of the combustion chamber or from other processes is passed, must be made of a heat-resistant material, for instance high-temperature resistant steel. Due to the great temperature differences with respect to other components of the plant, high thermal stresses can also occur.

Accordingly, it is the object underlying the invention to provide a process and a plant as mentioned above, which provide for the use of inexpensive fuels or hot waste gases and at the same time a gentle treatment of fluidizable substances in the reactor, wherein the loads acting on the reactor or the components remain limited.

In accordance with the invention, this object substantially is solved with a process, in which the gas and/or the gas supply tube are cooled with a coolant such that the wall of the gas supply tube has a temperature lower by at least 50° C. than the gas at the inlet of the gas supply tube facing away from the reactor interior. In other words, the gas and/or the gas supply tube is cooled with a coolant such that the fluidizable substances in the reactor are sufficiently heated, but the components of the reactor are not exposed to excessive thermal and mechanical loads. By charging the gas supply tube with a coolant, it is therefore possible to use a less expensive material for the gas supply tube despite the very high temperatures of the gas in the gas supply tube, as the same is subjected to lower temperature resistance requirements. This advantageous effect can further be increased in that as a result of cooling, the wall of the gas supply tube has a distinctly lower temperature, in particular lower by at least about 100° C., preferably by about 150° C., than the gas at the inlet of the gas supply tube. By means of cooling, the gas in the gas supply tube itself is hardly cooled, however, and the gas at the reactor-side outlet of the gas supply tube mostly is only cooler by less than 200° C., preferably less than 100° C. than at the inlet.

In accordance with a first embodiment of the invention, the coolant cannot get in direct contact with the gas in the gas supply tube during cooling. This provides for the use of coolants optimized in terms of their cooling properties, without having to consider interactions with the hot gas, for instance the waste gas of the combustion chamber, and/or the substances to be treated in the reactor.

Thus, water can for instance be used as coolant. To simplify the construction of the cooling means, the temperature of the water preferably is up to about 100° C., so that no appreciable pressure is built up. In principle, however, pressure-resistant cooling means are also possible, in which water from a steam system or from upstream regions is used for cooling the gas supply tube and/or the waste gas. Due to the partly only small heat-exchange surfaces, the heat gain for a steam system also is only small, however, when cooling the hot gas and/or the gas supply tube. However, the cooling effect is sufficient to protect the gas supply tube from being damaged and from excessive thermal loads.

Alternatively, heat transfer oils or other coolants are of course also possible, which preferably are advantageously used in other parts of the plant, e.g. for heating up other substances or as a secondary circuit for heat recovery.

Preferably, the coolant is passed through an annular and/or helical cooling duct formed on the inside and/or outside of the gas supply tube. Thus, not only the gas in the gas supply tube, but in particular the wall of the gas supply tube can be cooled to such an extent that no expensive, high-temperature resistant material must be used for the gas supply tube.

In a special embodiment, the material of the gas supply tube consists of a radiation-reflecting material or has a reflecting coating, e.g. tinplate, so that heating up by radiation is reduced.

In accordance with a further embodiment of the invention, the coolant gets in direct contact with the hot gas during cooling. The objective is to keep the flow of the hot gases away from the wall of the gas supply tube by selective and metered supply of the coolant.

The resulting thorough mixing of the hot gas, e.g. the waste gas of the combustion chamber, with the coolant, should be minimized and can effect a more efficient cooling of the gas at the edges of the gas supply tube. Thus, the gas generally enters the reactor with a slightly lower temperature, but the temperatures at the edge of the gas supply tube are much lower than the average temperature of the gas at the inlet of the gas supply tube.

In accordance with a development of this invention it is provided that the coolant is introduced into the gas supply tube and/or a portion of the reactor adjoining the gas supply tube and is mixed there with the hot gas. Thus, the coolant can be introduced into the gas supply tube or the reactor for instance from a perforated tube, a membrane and/or via an orifice plate. This allows a uniform cooling of the gas supply tube without the occurrence of temperature gradients generating thermal stresses. The supply of the coolant is effected such that there is only a minimum intermixture with the gas in the gas supply tube, and a boundary layer of cold coolant substantially is built up on the inside of the gas supply tube.

The gas supply tube can be shielded particularly efficiently from the gas passed through with high temperature, when the coolant is introduced into the gas supply tube such that a coolant layer enveloping the gas is at least partly formed. Preferably, the coolant flows along the inner wall of the gas supply tube or along a cooling means provided in the same and thus forms a cooler gas cushion between the hot gas and the gas supply tube.

In a further embodiment of the invention the coolant is introduced into the gas supply tube, e.g., by an orifice plate in which the orifices are distributed around the supply tube. It is preferred, that these orifices are formed in a way so that the coolant enters the gas supply tube in a tangential direction. In this case a very good and small film of coolant is formed around the wall of the supply tube.

As coolant which can also get in contact with the gas, ambient air is preferably used. However, any other gas can be used for this purpose, e.g., cooled and cleaned waste gas from other processes or process stages. What can be used in particular are gases which have a much higher viscosity or which must be supplied additionally for the reaction in the fluidized-bed reactor. In accordance with the invention, the coolant, for instance cooling gas, has a rather low temperature, preferably between about 0 and 400° C., particularly preferably below 200° C.

In another embodiment, the coolant is delivered in liquid or even solid form to the inner wall of the gas supply tube, where it is then preferably evaporated or sublimed and thereby forms a gas cushion or a liquid layer which protects the inner wall of the gas supply tube against the heat. Water is particularly useful here as coolant. In a further embodiment, this liquid or solid coolant is introduced within a gas stream, e.g., as droplets or line particles.

In accordance with the invention, the hot gas introduced into the reactor through the gas supply tube can come from another process, e.g. also from a heat exchanger. In this case, the gases in the gas supply tube have a temperature of about 600 to 1000° C. In the reactor, an internal combustion can take place, but due to the thermal loads caused by the gas supplied, the gas supply tube must be cooled. Depending on the temperature of the gas in the gas supply tube, far less heat-resistant and hence less expensive materials can also be used, e.g. steel which only is heat-resistant up to 600° C., preferably up to 500° C., particularly preferably only up to 450° C. (e.g. boiler plate, H2 steel).

As an alternative to heating the substances to be treated by a combustion directly inside the reactor or by supplying hot gas from another process, the waste gas of a combustion chamber upstream of the reactor, in which fuel and combustion air is burnt at temperatures of about 1000 to about 1500° C., can also be supplied to the reactor as hot gas. This leads to particularly high temperatures in the gas supply tube, which require a particularly efficient cooling and/or the use of heat-resistant materials, but this inventive decoupling of the combustion in the combustion chamber and the treatment of substances in the reactor provides for also using inexpensive fuels. Due to the interposed cooling, natural gas, petroleum or coal as well as biomass or waste materials thus can also be used as fuel, which require a distinctly higher ignition temperature or combustion temperature than is necessary or desirable for the treatment inside the reactor at a temperature of e.g. 500 to 700° C.

In the process of the invention, an ash-producing fuel can also be used as fuel, wherein a gas cleaning possibly is provided between the combustion chamber and the fluidized-bed reactor. The combustion can for instance be effected e.g. in a horizontal cyclone, in which ash of the fuel is separated from the hot waste gas and precipitated. This allows the use of inexpensive and locally available fuels. The choice of the fuel also is dependent on the requirements of the substance to be treated. Substances which have no increased requirements concerning the freedom from impurities can be calcined by ash-containing fuels, whereas substances which must remain free from impurities, e.g. white paper filler, must be treated with ash-free fuels.

Another alternative for heating the substances is the use of a waste gas, e.g., from an electric furnace. In this case the hot gases have a temperature of 1000° C. to 1900° C.

In accordance with one embodiment of the invention, the reactor is a fluidized-bed reactor, in which a stationary fluidized bed is annularly formed around the gas supply tube. In this case, a gas can be passed as coolant through a cooling tube provided around the gas supply tube and can subsequently be guided into a gas distributor provided below the stationary fluidized bed, so that the cooling gas can be introduced into the stationary fluidized bed as fluidizing gas via a tuyère bottom. To maintain the temperature inside the reactor within the temperature limits optimal for the treatment of substances, for instance in the case of clay calcination below about 700° C., the supplied quantity of the hot gas in the gas supply tube preferably is controlled and/or regulated on the basis of the temperature in the reactor.

The object underlying the invention furthermore is solved by a plant for the thermal treatment of granular solids, which includes a fluidized-bed reactor, in which the solids are introduced via a solids supply conduit and in which they are thermally treated substantially at a temperature of about 300° C. to about 1200° C., preferably of about 500° C. to about 700° C., and a gas supply tube, which for supplying process gas substantially centrally opens into the fluidized bed reactor from below. Preferably, a combustion chamber is provided upstream of the fluidized-bed reactor, in which fuel is burnt at a temperature of for instance 1000 to 1500° C. and which is connected with the fluidized-bed reactor via the gas supply tube. In accordance with the invention, a for instance annular cooling duct for cooling the gas supply tube and the process gas is at least partly associated to the gas supply tube, which is connected with a coolant source for supplying coolant with a temperature of below about 400° C., in particular below about 100° C. The flow cross-section of the cooling duct preferably is smaller than the flow cross-section of the gas supply tube, so that the coolant is strongly heated by the gas supply tube or the process gas. Due to the configuration of the plant of the invention with a cooling duct, e.g. simple steels can be used for the gas supply tube, which are heat-resistant up to about 800° C., preferably only up to about 700° C., particularly preferably up to about 650° C. (e.g. 16Mo3 steel). The use of expensive, highly heat-resistant chrome-nickel steels therefore can he avoided. At the same time, the temperature inside the reactor can be kept low, without having to renounce the use of inexpensive fuels, which require a higher ignition temperature and/or combustion temperature.

In another embodiment of the invention the plant comprises an electric furnace, and the waste gases of the electric furnace are supplied to a reactor, preferably a fluidized-bed reactor, in which solids are treated with at least a part of this waste gas.

In accordance with a preferred embodiment of the invention, the gas supply tube of the fluidized-bed reactor is annularly surrounded by a stationary fluidized bed, and the plant includes a gas distributor provided below the stationary fluidized bed, from which fluidizing gas is introduced into the stationary fluidized bed via a tuyère bottom. Above the gas supply tube and the stationary fluidized bed, a turbulence mixing chamber can be provided for the intensive mixing of the solids. The cooling duct of the invention at least partly constitutes an annular space between the gas distributor and the gas supply tube, wherein the cooling duct is connected with the gas distributor formed below the stationary fluidized bed of the fluidized-bed reactor. The gaseous coolant flowing through the cooling duct thus can also be used for fluidizing the stationary fluidized bed, and the heat dissipated from the gas supply tube is introduced into the reactor. By means of the configuration in accordance with the invention, according to which the cooling duct constitutes an annular space between the gas distributor and the gas supply tube, an increased flow velocity is achieved inside the cooling duct, so that a more efficient cooling of the gas supply tube or the gases flowing through the same is achieved.

In accordance with a development of this invention it is provided that the cooling duct includes a plurality of outlet openings distributed around the periphery, which open into the gas distributor. Alternatively, it is also possible that the cooling duct includes an outlet opening annularly formed around its periphery, which opens into the gas distributor. The at least one outlet opening can open into the gas distributor directly below the tuyère bottom.

In accordance with a further embodiment of the invention, the plant of the invention includes a cooling tube in the gas supply tube such that between the gas supply tube and the cooling tube an annular cooling duct is formed. Therefore, the gas supply tube is cooled on its inside by the coolant flowing in the annular cooling duct.

Particularly preferably, outlet openings are provided in the cooling tube for connecting the cooling duct with the reactor interior or the interior of the gas supply tube. In this way, a coolant layer enveloping the waste gas of the combustion chamber and flowing along the inner wall of the gas supply tube or of the cooling tube can be formed, which as a gas cushion prevents an excessive heating of the gas supply tube or of the, cooling tube.

When the fluidized-bed reactor constitutes a Venturi reactor, the cooling tube can open into a flared portion with outlet openings for connecting the cooling duct with the reactor interior. Preferably, the portion of the cooling tube adjoining the gas supply tube extends substantially parallel to the likewise flared bottom of the reactor. In this way, not only the gas supply tube, but also the bottom of the reactor can be cooled.

A particularly efficient cooling can be achieved by using water as coolant. Preferably, on the inside or outside of the gas supply tube, a cooling duct is at least partly provided, which is connected with a coolant source containing water as coolant with a temperature of up to about 100° C. The cooling duct can for instance be formed helically and extend around the gas supply tube in the manner of a cooling coil.

To additionally protect the material of the gas supply tube against an excessive thermal load due to the waste gases of the combustion chamber, a studding made of gunned concrete or some other suitable thermal insulating coating can be provided on the inside of the gas supply tube. Even at temperatures of the waste gas of the combustion chamber of 1300° C. and more, the loads of the gas supply tube thus can be minimized.

Preferably, a gas cleaning means is associated to the combustion chamber in the plant of the invention. The combustion chamber can constitute a horizontal cyclone.

Furthermore, the invention relates to the use of a material with low heat resistance for instance in the gas supply tube of a plant or of a method as mentioned above.

The invention will subsequently be explained in detail by means of embodiments and with reference to the drawings. All features described and/or illustrated per se or in any combination form the subject-matter of the invention, independent of their inclusion in the claims or their back-reference.

In the drawing:

FIG. 1 schematically shows a plant in accordance with a first embodiment of the invention,

FIG. 2 shows an enlarged representation of a detail of the plant as shown in FIG. 1,

FIG. 3 shows a detail of a plant in accordance with a second embodiment of the invention,

FIG. 4 show a detail of a plant in accordance with a third embodiment of the invention,

FIG. 4 a is a sectional view along line A-A in FIG. 4,

FIG. 5 shows a detail of a plant in accordance with a fourth embodiment of the invention,

FIG. 6 shows a detail of a plant in accordance with a fifth embodiment of the invention, and

FIG. 7 shows a detail of a plant in accordance with a further embodiment of the invention.

The plant for the thermal treatment of granular solids, such as for clay calcination, which is shown in FIG. 1, includes a fluidized-bed reactor 1 in whose reactor interior 2 the solids are subjected to a chemical and/or physical treatment.

A gas supply tube (central tube) 3, which is connected with a combustion chamber 4, opens into the reactor interior 2. As indicated by the arrows in FIG. 1, fuel and gas are supplied to the combustion chamber. The waste gas heated to a temperature of up to 1500° C. during the combustion is passed from the combustion chamber 4 via the gas supply tube 3 into the reactor interior 2.

In the reactor 1, a tuyère bottom 5 is provided, which is associated to a gas distributor 6. Through a conduit 7, fluidizing gas is introduced into the gas distributor 6, which reaches the reactor 1 via the tuyère bottom 5. Above the tuyère bottom 5, the gas supply tube 3 is surrounded by an annular stationary fluidized bed, which is intermixed by the fluidizing gas. Furthermore, a recirculation cyclone 8 is schematically indicated in FIG. 1, in which solids discharged from the reactor 1 are separated from the waste gas of the reactor 1 and can possibly be recirculated into the reactor 1.

The formation of the gas distributor 6 and of the gas supply tube 3 of the plant as shown in FIG. 1 is illustrated in detail in FIG. 2. The gas supply tube 3 partly is surrounded by a cooling tube 9, so that an annular cooling duct 10 is formed between the outside of the gas supply tube 3 and the inside of the cooling tube 9. A coolant, for instance ambient air, is passed through the cooling duct 10, thereby cooling the wall of the gas supply tube 3 and hence also the waste gas of the combustion chamber 4, which is flowing through the same. As shown in FIG. 2, the cooling tube includes a plurality of outlet openings 11 distributed around the periphery in the vicinity of the tuyère bottom 5, which open into the gas distributor 6. The ambient air used as coolant thus can be introduced into the reactor interior 2 as an additional fluidizing gas. In contrast to the embodiment shown in FIG. 2, in which the coolant is introduced cocurrently with respect to the gas supply tube, it is also possible to countercurrently guide the coolant. The guidance of coolant can be configured such that the part of the gas supply tube protruding into the reactor is cooled first and then the coolant is deflected downwards, so as to countercurrently flow downwards.

Another embodiment of the invention is shown in FIG. 3, wherein the components identical with the embodiment described above are provided with the same reference numerals.

In this embodiment, the cooling tube 9 in turn is arranged annularly, surrounding the central gas supply tube 3, so that an annular cooling duct 10 is formed between the gas supply tube 3 and the cooling tube 9. The gas supply tube 3 partly is provided with outlet openings 12, so that a coolant flowing through the annular cooling duct 10 can get into the interior of the central gas supply tube 3. In doing so, the coolant can form a coolant layer flowing along the inner surface of the gas supply tube 3 and thus protect the material of the gas supply tube 3 against an inadmissibly high heating.

FIGS. 4 and 4 a show an alternative to the embodiment according to FIG. 3 wherein only some outlet openings 12′ are provided at one or two levels around the gas supply tube 3. These openings 12 are preferably provided in a way that the coolant enters the gas supply tube 3 in a tangential direction.

In the embodiment of FIG. 5, the reactor 1′ constitutes a Venturi reactor. The cooling tube 9, which is provided inside the central gas supply tube 3, protrudes into the sloped lower region of the reactor 1′ and substantially is funnel-shaped like this region. In the funnel-shaped portion of the cooling tube 9, a plurality of outlet openings 12 are formed, so that a coolant, for instance ambient air, can get into the interior 2 of the reactor 1′. Alternatively, however, it is also possible that the coolant is not introduced into the Venturi or annular-fluidized-bed reactor, but is employed in other parts of the process, e.g. as preheated air for the combustion chamber.

The embodiment shown in FIG. 6 has a similar construction as the embodiment of FIG. 3. However, on the outside of the central gas supply tube 3 a helical cooling duct 13 is formed, through which water is passed as coolant. In contrast to the embodiments described above, the cooling duct 13 is configured such that the water guided in the same cannot get into the central gas supply tube 3 or the interior 2 of the reactor.

In the embodiment shown in FIG. 7, which substantially corresponds to the embodiment of FIG. 6, a so-called studding 14, i.e. a coating with a gunned concrete or some other suitable thermal insulating coating is additionally provided on the inside of the central gas supply tube 3. In this way, the central gas supply tube is shielded from the inside by the studding 14 and cooled from the outside by the cooling duct 13.

By means of the cooling of the central gas supply tube 3 as described above, it is achieved that the waste gas from the combustion chamber 4 is cooled considerably from a temperature of about 1000 to 1500° C., so that the waste gas heats the solids treated in the reactor 1 to a temperature of about 500 to about 700° C.

EXAMPLE 1

In a reactor as shown in FIG. 1, a gas with a temperature of 1000° C. enters the gas supply tube. By supplying a cooling gas, here nitrogen as inert gas, with a temperature of 100° C., the wall of the gas supply tube is cooled to about 600° C. At the same time, the temperature of the gas in the gas supply tube is cooled to about 950° C.

EXAMPLE 2

In a reactor as shown in FIG. 5, gas with a temperature of 850° C. is introduced into the gas supply tube. By supplying a cooling gas, here air, with a temperature of 30° C., the wall of the gas supply tube is cooled to about 650° C. As a result, a brick lining of the wall or the use of high-temperature resistant stainless steels can be omitted.

EXAMPLE 3

In a reactor as shown in FIGS. 4 and 4 a hot gas from an electric furnace with a temperature of about 1400° C. is introduced into the gas supply tube. Cooling gas having a temperature of about 100° C. is introduced into the gas supply tube 3 tangentially via openings 12, so that a small film of cooling gas is formed around the wall of the gas supply tube 3. The temperature of the wall of the gas supply tube 3 never exceeds 650° C., whereas the gas enters the fluidized-bed reactor with a temperature above 1000° C. In this way e.g. iron ore can be preheated and/or prereduced in the fluidized-bed reactor at a temperature of about 900-1100° C.

List of Reference Numerals:

1 fluidized-bed reactor

1′ Venturi reactor

2 reactor interior

3 gas supply tube (central tube)

4 combustion chamber

5 tuyère bottom

6 gas distributor

7 conduit

8 recirculation cyclone

9 cooling tube

10 cooling duct

11 outlet opening

12, 12′ outlet opening

13 cooling duct

14 studding 

1-26. (canceled)
 27. A process for at least one of a chemical and a physical treatment of fluidizable substances in a reactor, the process comprising: introducing a hot gas into an interior of the reactor through a gas supply tube; and cooling at least one of the hot gas and the gas supply tube with a coolant, wherein the cooling is performed by contacting the hot gas with the coolant so as to provide a temperature of a wall of the gas supply tube at least 50° C. lower than a temperature of the gas at an inlet of the gas supply tube facing away from the interior of the reactor.
 28. Process as recited in claim 27, wherein the reactor is a fluidized-bed reactor.
 29. Process as recited in claim 27, wherein the coolant is water with a temperature of up to 100° C.
 30. Process as recited in claim 27, wherein the coolant is introduced from at least one of a perforated tube and an orifice plate into at least one of the gas supply tube and a portion of the reactor adjoining the gas supply tube so as to mix the coolant therein with the hot gas.
 31. Process as recited in claim 27, wherein the coolant is introduced into the gas supply tube so as to at least partly form a coolant layer enveloping the hot gas, wherein the coolant layer flows along an inner wall of the gas supply tube.
 32. The process as recited in claim 27, wherein the coolant enters the gas supply tube tangentially.
 33. The process as recited in claim 27, wherein the coolant is ambient air.
 34. The process as recited in claim 27, further comprising a combustion chamber disposed upstream of the reactor, wherein a fuel and combustion air are supplied into the combustion chamber and burned at a temperature of 1,000° C. to 1,500° C., and wherein a waste gas of the combustion chamber is supplied to the reactor as the hot gas through the gas supply tube.
 35. The process as recited in claim 27, wherein the reactor is a stationary fluidized bed reactor with a tuyèle bottom, the statationary fluidized bed being formed annularly around the gas supply tube in the reactor, the cooling tube is disposed around the gas supply tube, and a gas distributor is disposed below the stationary fluidized bed, and the coolant is a gas, the gas being passed through the cooling tube into the gas distributor and into the stationary fluidized bed as fluidizing gas via the tuyère bottom.
 36. The process as recited in claim 35, wherein a quantity of one or more of the hot gas and the waste gas of the combustion chamber is controlled based on the temperature in the reactor.
 37. The process as recited in claim 35, further comprising cleaning the gas between the combustion chamber and the fluidized-bed reactor and wherein ash-producing fuels are used as the fuel.
 38. The process as recited in claim 27, wherein the hot gas has a temperature of about 1,000° C. to 1,900° C. and is produced in an electric furnace.
 39. The process as recited in claim 27, wherein the fluidizable substances are treated in the reactor at a temperature of about 900° C. to 1,100° C.
 40. A plant for at least one of a chemical and a physical treatment of granular solids, the plant comprising: a fluidized-bed reactor with a reactor interior; a solids supply conduit configured to introduce the granular solids into the fluidized bed reactor; a gas supply tube configured to supply a process gas from below, wherein the gas supply tube opens substantially centrally into the fluidized-bed reactor; a cooling tube disposed relative to the gas supply tube so as to form an annular cooling duct between the gas supply tube and the cooling tube, the annular cooling duct being configured to cool the gas supply tube and the process gas, the annular cooling duct being connected with a coolant source configured to supply a coolant with a temperature of below about 400° C.; and outlet openings disposed in the cooling tube so as to connect the annular cooling duct with the reactor interior.
 41. The plant as recited in claim 41, wherein the gas supply tube of the fluidized-bed reactor is annularly surrounded by a stationary fluidized bed, the stationary fluidized bed including a gas distributor disposed below the stationary fluidized bed, the gas distributor being configured to introduce a fluidizing gas into the stationary fluidized bed via a tuyère bottom, and a turbulence mixing chamber disposed above the gas supply tube and the stationary fluidized bed, the turbulence mixing chamber being configured to intensively mix the granular solids, wherein the annular cooling duct at least partly defines an annular space between the gas distributor and the gas supply tube, and wherein the annular cooling duct is connected with the gas distributor.
 42. The plant as recited in claim 41, wherein the annular cooling duct includes a plurality of outlet openings distributed around a periphery, the outlet openings opening into the gas distributor.
 43. The plant as recited in claim 42, wherein the outlet opening open into the gas distributor below the tuyère bottom.
 44. The plant as recited in claim 40, wherein the fluidized-bed reactor is a Venturi reactor in which the cooling tube opens into a flared portion with the outlet openings configured to connect the annular cooling duct with the reactor interior, wherein the cooling tube adjoins the gas supply tube and extends substantially parallel to the flared bottom of the reactor.
 45. The plant as recited in claim 40, wherein the annular cooling duct is disposed on at least one of an inside or an outside of the gas supply tube, the annular cooling duct being connected with the coolant source, the coolant including water having a temperature of up to about 100° C.
 46. The plant as recited in claim 45, wherein the annular cooling duct is helically shaped.
 47. The plant as recited in claim 40, wherein an inside of the gas supply tube further includes a studding comprising gunned concrete.
 48. The plant as recited in claim 40, further comprising a gas cleaning means for the combustion chamber.
 49. The plant as recited in claim 40, wherein the gas supply tube includes a wall material exhibiting a heat resistance of up to 650° C. 